In recent years, portable electronic devices such as mobile phones and PDAs (Personal Digital Assistants) are in wide use. As the display sections of portable electronic devices, liquid crystal display devices are used, which have advantages of being thin and light-weight and having low power consumption.
Generic liquid crystal display devices utilize polarizers, and thus have a relatively low efficiency of light utilization. Therefore, in order to realize bright display, it is necessary to increase the intensity of externally-entering light, e.g., a backlight. However, when the intensity of light from a backlight is increased, the power consumption increases. Therefore, liquid crystal display devices have been proposed which realize an improved efficiency of light utilization without employing polarizers, this being done by using a scattering-type liquid crystal layer which switches between a scattering state and a transparent state in accordance with changing voltages.
For example, Patent Document 1 discloses a projection-type liquid crystal display device having a scattering-type liquid crystal layer. A scattering-type liquid crystal layer switches between a transparent state and a scattering state based on voltage, whereby switching between transmission and shielding of projection light is performed.
Patent Document 2 discloses a transmission-type liquid crystal display device having a scattering-type liquid crystal layer. In this transmission-type liquid crystal display device, by using a scattering-type liquid crystal layer which is provided between a liquid crystal panel and a backlight, the directivity of light from the backlight is switched by switching between convergence and scatter of the light emitted from the backlight.
In such a projection-type liquid crystal display device and a transmission-type liquid crystal display device, when a voltage is applied across the scattering-type liquid crystal layer, the scattering-type liquid crystal layer takes a transparent state, whereby the luminance in the frontal direction is increased. Conversely, when no voltage is applied across the scattering-type liquid crystal layer, the scattering-type liquid crystal layer takes a scattering state, whereby the luminance in the frontal direction is decreased.
Other than such a projection-type liquid crystal display device and a transmission-type liquid crystal display device, a reflection-type liquid crystal display device having a scattering-type liquid crystal layer is also known (see, for example, Patent Document 3). A reflection-type liquid crystal display device does not include any backlight or the like, but performs displaying by reflecting light entering from the surroundings, thereby realizing a further reduction of power consumption.
The reflection-type liquid crystal display device disclosed in Patent Document 3 includes a scattering-type liquid crystal layer, a reflection plate having a low-refractive index layer, and a light-absorbing layer. When displaying black, the scattering-type liquid crystal layer takes a transparent state, and the incident light from the surroundings travels through the scattering-type liquid crystal layer and the low-refractive index layer to be absorbed by the light-absorbing layer. In this case, since the incident light does not reach the viewer, the viewer perceives black. On the other hand, when displaying white, the scattering-type liquid crystal layer takes a scattering state, and the light entering from the surroundings is scattered by the scattering-type liquid crystal layer, and thereafter receives total reflection at the interface between the low-refractive index layer and its retainer, thus returning toward the viewer. When the incident light thus reaches the viewer, the viewer perceives white.
There is also known a reflection-type liquid crystal display device having, as a reflective member, a retroreflection member which retroreflects light (for example, Patent Documents 4 and 5). In the present specification, such a liquid crystal display device will also be referred to as a retroreflection-type liquid crystal display device. In the retroreflection-type liquid crystal display devices disclosed in Patent Documents 4 and 5, the scattering-type liquid crystal layer takes a scattering state when displaying white, so that light from the light source is scattered by the scattering-type liquid crystal layer so as to reach the viewer. As a result, the viewer perceives white. On the other hand, when displaying black, the scattering-type liquid crystal layer takes a transparent state, so that light from the light source is reflected by the retroreflection plate so as to return to the light source, and thus the light from the light source does not reach the viewer. As a result, the viewer perceives black.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 6-222331    [Patent Document 2] Japanese Laid-Open Patent Publication No. 11-142819    [Patent Document 3] Japanese Laid-Open Patent Publication No. 2002-333610    [Patent Document 4] Japanese Laid-Open Patent Publication No. 2002-107519    [Patent Document 5] Japanese Laid-Open Patent Publication No. 2006-215106